21219797 has 4 divisors (see below), whose sum is σ = 21429996. Its totient is φ = 21009600.

The previous prime is 21219787. The next prime is 21219799. The reversal of 21219797 is 79791212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17255716 + 3964081 = 4154^2 + 1991^2 .

It is a cyclic number.

It is not a de Polignac number, because 21219797 - 2¹⁸ = 20957653 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21219797.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21219799) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 104948 + ... + 105149.

It is an arithmetic number, because the mean of its divisors is an integer number (5357499).

Almost surely, 2^21219797 is an apocalyptic number.

It is an amenable number.

21219797 is a deficient number, since it is larger than the sum of its proper divisors (210199).

21219797 is a wasteful number, since it uses less digits than its factorization.

21219797 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 210198.

The product of its digits is 15876, while the sum is 38.

The square root of 21219797 is about 4606.4950884593. The cubic root of 21219797 is about 276.8516237162.

The spelling of 21219797 in words is "twenty-one million, two hundred nineteen thousand, seven hundred ninety-seven".